The iPhone has a touchscreen and one forward-facing button, which is sort of testament to Apple's design ethos of simplicity and aesthetics. But HTC devices tend to have several buttons, and my Nexus One has 4 buttons and a clickwheel. Then there are the Windows Phone 7 devices coming out soon with 3 buttons.

What's going on here? Is there any information available as to what decisions are made regarding how many buttons are good for touch devices like smartphones? It's fairly apparent why iPhone went with one button (part of their vision for the iPhone was reducing the number of buttons, but they conceded one largely for accessibility reasons and for having a fallback in the case of a faulty screen). But why are HTC and other phone manufacturers deviating from that first design? Is it principle? User research? Stubbornness?

7 Answers
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I don't remember the specifics, but I do know that with Windows Phone 7, they DID do significant research in coming up with the minimum required specs for their phones. When I was at a developer event for Windows Phone 7, they went into a lot of detail ont he design process and the research that they did in coming up with the design.

For the record, I don't believe that the iPhone's single physical button really is the best interface, having used it and several other smart phones. Both as a user and a developer, it is actually extremely limiting. Simple, yes, but simple isn't always better. In fact, having only a single physical button makes some things more complex.

Can you link to or reference said research?
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Rahul♦Sep 15 '10 at 15:10

1

No - just like your Amazon UI question, that research is proprietary. Microsoft is not going to share their usability research with the general public. You can find and ask anyone on their design team and I'm sure they'll share details, but you aren't going to get the actual research from them.
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Charles BoyungSep 15 '10 at 15:51

My belief (and feel free to correct me if I'm wrong) is that smartphone makers use buttons because buttons don't move or disappear. A button is is useful for functions that you might want to activate at any time, in any application (e.g. volume keys, silent switch, power button — though those aren't usually front-facing).

The home button on an iPhone is always in the same place and always brings you home.

The back button on an Android device always takes you back to the previous screen or task, the home button always takes you home, the menu button shows you more options, and the search button shows a search field. I think that the usefulness of the latter two is debatable.

A trackball or touchpad lets you navigate with your hand in a predictable position, making predictable motions. I think it's a vestige at this point. It's only useful on Android to manipulate and select text, and the iPhone's text selection mechanism makes even that obsolete.

Yes, this much is clear, but the question isn't why do people use buttons, but why do certain phones have several vs. one? Or 4 vs 3?
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Rahul♦Sep 16 '10 at 5:59

I think the "back" button's usefulness is debatable and confusing in some situations (e.g. should it take you back to the app's main screen or to the external application you came from?). The "menu" button, on the other hand, is extremely useful, as it frees up screen real-estate, and provides a consistent way to reach less-used options.
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dbkkJun 22 '11 at 8:27

@Rahul maybe it's because some people hate all buttons with a passion, while others like something they can find without looking. Having none accommodates one end of the spectrum; having 3/4 the other, having 1 is kind of a compromise. Don't assume that other people are at all like you in liking or hating buttons; the range of opinions is vast.
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romkynsMar 5 '14 at 18:57

Overview

Looking at the innovations made by Apple and HTC as Apple moved from iPod to iPhone and HTC from personal organizers to mobile phones gives some insight into the design process. It's necessarily speculative, until someone from the inside gives a definitive answer.

Test bias can explain a lot. If you don't test the pinch-to-zoom gesture, dedicated buttons for zoom will look better than if you do. You won't test that pinch-to-zoom gesture, if you're still thinking 'resistive screens'. Resistive screens are mono-touch.

Test bias can explain a lot. If you never test apps together, only in isolation, you have a problem a bit like the problem with the sip test described by Malcolm Gladwell. A test that looks at UX one app at a time is more likely to determine that each app needs more buttons.

Detail

But why are HTC and other phone
manufacturers deviating from that
first design?

It's NOT a first design.

Using 'too many buttons' is mostly down to history in the two companies and the way designs evolve. Apple moved from a low cost non-touch-screen MP3 player to phone. HTC moved from a premium non-touch-screen personal organizer to phone.

Why did Apple shed buttons? Apple pay attention to cost reduction early in the design. It was particularly important for iPod. They got in to these capacitative touch technology/chipsets via iPod 'wheel' which was largely motivated by reduced manufacturing costs. A capacitative wheel gets more input flexibility for a much lower price than lots of quality buttons do. Unlike a resistive screen capacitative touch is multi-touch. It's a good tradeoff, using smart electronics to replace mechanics. As well as reducing cost it's also good for reducing size and weight. From their experience with click-wheel Apple knew that touch screen could make front buttons redundant. The one front facing button is just the last remnant of the click-wheel. Their click-wheel experience, and cost reduction, guided them on their path to minimalism.

Why didn't Microsoft/HTC shed buttons? They were building on their own history and experience. The idea of having an abundance of buttons is the norm in for example HTC's iPAQ (five front buttons). Their existing software relied on it. Is it so surprising that their usability studies didn't pick up the opportunities for fewer buttons? Users can only rate options that are put before them. They used versions of their existing software. Microsoft/HTC engineers were thinking in terms of clicking not sliding - whilst Apple engineers had already gone beyond the sliding in click-wheel to multi-touch. If you've got multi-touch you don't need a zoom button. This is the crucial point. The low button count options Microsoft would have presented to user testing would not have been as good as Apple's, and in particular would have been less good at using sliding. The answers they would have got from user testing would have told them clicking was important, and more buttons were better.

The history argument also answers why Apple put that button on the front at all. It isn't needed there! With the right software the only buttons that are needed still are one's that are used when the screen is dark, and they can and should be side buttons. Tablets are going in that direction.

Edit

A related test bias issue: User testing one application at a time will introduce a bias in favor of dedicated buttons. It's only when you're using your calendar that a dedicated 'record' and dedicated 'send' button that aren't being used starts to niggle. This is where vision helps. Having an overall vision for the product you are more likely to test and refine the vision as an integrated whole, rather than blindly build a solution by combining items tested only in isolation. The vision thing is a cultural difference between Apple and Microsoft.

I've said that Apple offered better options for touch for users to try, and hence saw better user satisfaction in testing. Apple's killer touch feature was of course zooming using multi-touch pinch gesture. If, as Microsoft did, you have mono touch you can't do that, so on mono-touch their user tests would rate a button to zoom-in or zoom-out more strongly than in Apple's tests. Multi-touch didn't come to Windows mobile (HTC) until early 2010. The pinch gesture became an Apple patent in 2009.

Cost Reduction

Keeping manufacturing costs down is only one of several competing driving forces in design. Sometimes the trade-offs swing in favor of the cheap option - a built-in battery is cheaper smaller and lighter than a replaceable one - fewer buttons are cheaper - black is cheaper - because a black background extends battery life. It's not minimalism or aesthetics that caused the switch from white to black. It's not minimalism that advertised the built-in-obsolescence of yesterday's iPhone by giving it a built-in battery.

Sometimes the trade-offs swing the other way. Capacitative screens are more expensive to make than resistive. Capacitative is more responsive but less accurate than resistive. They're worth it because they enable multi-touch, a better UX and fewer buttons.

Very speculative, but I like your line of thinking.
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Rahul♦Jun 2 '11 at 15:54

I think Apple is one of those few companies that designs well for use and for manufacture & maintenance, but I find it hard to believe that cost reduction is the primary driver behind their quest for minimalism.
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Todd SielingJun 5 '11 at 6:16

@Todd - Apple are great at looking at the product as a whole. Their quest is desirable profitable products. Minimalism is prestidigitation, misdirection. If they were truly minimalist through and through they would not encourage a gazillion apps to download.
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James CrookJun 5 '11 at 9:41

Android smartphones still have the 4 standard buttons (home, back, menu, and search), but Honeycomb tablets don't. This direction was made for tablets, the newer Android devices, when Matias Duarte from Palm joined. Learn about it here. You'll also learn from there that the new buttonless approach will happen also for smartphones. Rumor has it that this will be introduced in Ice Cream Sandwich, Android's next major version that's designed for both smartphones and tablets. With this new approach, the faces of Android devices will be buttonless, unlike the existing iOS ones.

There are also rumors that future iOS devices will be buttonless and that the home button's functions will be done with gestures.

Android doesn't try to be simple.
Most android users probably don't even know that they get a different behavior when they do a long press on the start instead of doing a short press.
The menu button allows a developer to use more screen estate without requiring the user to guess gestures by hiding menu elements.

When it comes to the search button, Google is a search company. They want people to search and therefore make it easy to search.

Hardware buttons are re-assuring to the user, as long as they behave consistently and predictably. It makes sense for certain frequently used functions to be universally accessible regardless of where you are.

I'm a Windows Phone 7 user, and two ("back" and "home") of the three buttons it uses behave as such and are invaluable. The odd one out is the schizophrenic "search" button which is contextual and so I'm never sure what to expect when I press it; as a result, I generally avoid using it.